>>1681924cheap cranks like that have riveted chainrings, not ones attached with chainring bolts. So you can't remove the chainrings. So you would need a new crank. If you're changing the crank on an old bike you'd probably want to change the bottom bracket too.
It would be much simpler to simply fix the front shifting. Replace the dead shifter (if it's really dead, and not just the cable, and maybe spraying inside with some wd40) with a simple friction unit like this, for very very cheap. All it's doing is pulling cable.
https://www.aliexpress.com/item/32999123125.htmland yes tires rot out. Infact after 30 years in a barn your grease will have dried out in all the bearings and the cables will be fucked too. The bike warrants a complete overhaul. I suggest you look at RJ the bike guy videos on youtube for tutorials on each thing.
